A semiconductor package is a metal, plastic, glass, or ceramic casing containing one or more semiconductor electronic components typically referred to as integrated circuit (IC) die. Individual discrete IC components are formed using known semiconductor fabrication techniques (e.g., CMOS) on silicon wafers, the wafers are then cut (diced) to form individual IC die, and then the IC die are the assembled in a package (e.g., mounted on a package base substrate). The package provides protection against impact and corrosion, holds the contact pins or leads which are used to connect from external circuits to the device, and dissipates heat produced in the IC die.
A micro-spring package is one type of semiconductor package in which electrical connections between the IC die and the package base substrate are provided by way of tiny curved spring metal fingers known as “micro-springs”. Micro-springs are batch-fabricated on a host substrate (i.e., either the IC die or the package base substrate), for example, using stress-engineered thin films that are sputter-deposited with a built-in stress gradient, and then patterned to form individual flat micro-spring structures having narrow finger-like portions extending from associated base (anchor) portions. The narrow finger-like portions are then released from the host substrate (the anchor portion remains attached to the substrate), whereby the built-in stress causes the finger-like portions to bend (curl) out of the substrate plane with a designed radius of curvature, whereby the tip end of the resulting curved micro-spring is held away from the host substrate. The micro-spring package utilizes this structure to make contact between the host substrate (e.g., the IC die) and a corresponding package structure (e.g., the package base substrate) by mounting the IC die such that the tip ends of the micro-springs contact corresponding contact pads disposed on the corresponding package structure.
Current methods for securing IC dies to base substrates using micro-springs requires the use of adhesives or bulky custom mechanical clamps. Adhesives are avoided as much as possible in high reliability electronics packaging and military applications because of organic outgassing risks, which limit ultimate reliability.
Ribbon bonds are metal connectors utilized to provide electrical connections between IC die and support substrates in some semiconductor packaging applications that require high power and high frequency packaging connections. Similar to wire bonds, ribbon bonds are only applied to the front (active) side metal of an IC die, and are not used in flip-chip-type packaging arrangements (i.e., where the front/active IC die surface faces the support structure).
What is needed is a low-cost method for securing an IC die to a support structure using micro-springs that avoids the need for adhesives.